Greg Salvesen

Accretion disc dynamo activity in local simulations spanning weak-to-strong net vertical magnetic flux regimes

Strongly magnetized accretion discs around black holes have attractive features that may explain enigmatic aspects of X-ray binary behaviour. The structure and evolution of these discs are governed by a dynamo-like mechanism, which channels part of the accretion power liberated by the magnetorotational instability (MRI) into an ordered toroidal magnetic field. To study dynamo activity, we performed three-dimensional, stratified, isothermal, ideal magnetohydrodynamic shearing box simulations. The strength of the self-sustained toroidal magnetic field depends on the net vertical magnetic flux, which we vary across almost the entire range over which the MRI is linearly unstable. We quantify disc structure and dynamo properties as a function of the initial ratio of mid-plane gas pressure to vertical magnetic field pressure,

Spectral hardening as a viable alternative to disc truncation in black hole state transitions

\beta_0^{\rm mid} = p_{\rm gas} / p_B

A physical model for state transitions in black hole X-ray binaries

. For

Strongly magnetized accretion discs require poloidal flux

10^5 \geq \beta_0^{\rm mid} \geq 10

Quantifying energetics and dissipation in magnetohydrodynamic turbulence

the effective

Convective quenching of field reversals in accretion disc dynamos

\alpha

A deep XMM-Newton observation of the quasar 3C 287

-viscosity parameter scales as a power-law. Dynamo activity persists up to and including

SHOCK SPEED, COSMIC RAY PRESSURE, AND GAS TEMPERATURE IN THE CYGNUS LOOP

\beta_0^{\rm mid} = 10^2

Rethinking Black Hole Accretion Discs

, at which point the entire vertical column of the disc is magnetic pressure-dominated. Still stronger fields result in a highly inhomogeneous disc structure, with large density fluctuations. We show that the turbulent steady state

Energetics and dissipation in the magnetised Kelvin-Helmholtz instability: the non-linear regime

\beta^{\rm mid}